Preheat oven to 350 F. Generously butter/grease and flour an 8x4 loaf pan.TIP - Whenever I grease and flour a loaf pan for quick bread, I always wipe away the top 1/2-3/4” of flour with a piece of paper towel. This can help the bread pull away from the sides and dome in the center better.
Whisk together cake flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice.
With a stand mixer, beat butter and brown sugar on medium speed until creamy.
6.35 ounces packed brown sugar, 1/2 cup unsalted butter
Add eggs and vanilla and beat just until combined.
1 teaspoon pure vanilla extract, 2 large eggs
Beat in pumpkin and bananas, beating just until combined.
4.5 ounces pumpkin puree, 2 overripe bananas
With a rubber spatula, stir in half of the dry ingredients. Stir in the buttermilk. Stir in remaining dry ingredients. Do not overmix, it’s okay if there are small traces of flour still showing.
2 ounces buttermilk
If adding chips, nuts, or fruit, fold them into the batter now.
Let batter rest 30 minutes. This allows the oven to get nice and hot as well.
Scrape batter into the prepared loaf pan. Place loaf pan on an insulated baking sheet.
Bake in preheated oven for 60–75 minutes, or until a butter knife poked into the center comes out clean.
Remove from oven and allow to cool in pan for 10 minutes, then remove to wire rack to cool completely.
While you wouldn’t think there’s a science to mashing a banana, the amount of mashing you do CAN affect the science of the baking process. Be sure to mash them up well, large chunks of banana can cause moisture pockets. This can affect the rise of your bread and make you think it isn't done. If you insert a toothpick into a section with a moisture pocket, you may continue baking and end up drying out your quick bread.
You should measure cake flour the same way you measure flour, by either weighing it or using the scoop and sweep method. Cake flour is finer than all purpose flour, which means it's even more important to not overmeasure. I highly recommend weighing it and using a kitchen scale.